GI Complications Associated with Elective General Anesthesia

Nelson said the team found that GI dysfunction occurred in 36 of the 416 procedures (about 8.7% of cases).

Photo: Anne M. Eberhardt/The Horse

Most horse owners are familiar with the risks associated with equine general anesthesia, which range from the dangers of recovery to death. Another common complication is colic. And researchers recently took their understanding of post-anesthetic colic a step further by completing a retrospective study on the topic.

Brad Nelson, DVM, MS, a PhD candidate at the Colorado State University (CSU) College of Veterinary Medicine, presented a study in which he evaluated the risk factors associated with gastrointestinal (GI) dysfunction in horses undergoing elective procedures under general anesthesia at the 2013 American Association of Equine Practitioners' Convention, held Dec. 7-11 in Nashville, Tenn.

Post-anesthetic colic (PAC) is well-recognized; occurs in 3-6% of horses; and can develop after a variety of procedures in which veterinarians employ general anesthesia, including surgery, computed tomography, and MRI. Nelson said elective surgeries are known to have complications; better characterizing what complications occur and how frequently could help veterinarians decrease the complication rate and also help them better educate clients on risks associated with their horses' surgical and anesthetic procedures.

Nelson and colleagues decided to perform a retrospective study to evaluate how many horses developed PAC or reduced fecal output that required treatment, and to identify potential risk factors for GI dysfunction.

The team evaluated 389 systemically healthy adult horses of varying breeds undergoing 416 procedures requiring general anesthesia over a three-year period at CSU. They evaluated:

Intra-anesthetic values (the horse's positioning on the table, anesthetic maintenance, lidocaine and dobutamine administration, blood pressure, total anesthetic time, arterial lactate, and recovery length); and

Post-anesthetic values (drugs administered after recovery, vital signs after recovery and the next day, time to first fecal passage, and total fecal output in 24 hours).

Nelson said the team found that GI dysfunction occurred in 36 of the 416 procedures (about 8.7% of cases). Of those:

14 horses had decreased fecal output without signs of colic;

Six horses developed colon impactions;

Four had cecal dysfunction or impaction; and

Veterinarians couldn't reach a diagnosis in 12 horses; Nelson said these were most likely instances of gas or spasmodic colic.

All but one of the horses that developed complications survived discharge, Nelson said. The remaining horse was euthanized after developing cecal dysfunction and uncontrollable pain. The surviving horses were treated for an average of 21.7 hours before resolution.

Nelson and colleagues identified the following risk factors for PAC:

Breed—33% of Arabians developed GI dysfunction. "However, there were proportionally fewer Arabian horses in this study and this percentage may be an overestimate of the true prevalence," Nelson cautioned;

Arterial lactate levels—Horses with increased lactate levels which might indicate that oxygen levels are low during anesthesia were more likely to develop GI dysfunction;

Positioning—Horses placed in right lateral recumbency (on their right sides) were significantly more likely to develop GI dysfunction; however, Nelson noted that the difference is not likely clinically relevant. When simply comparing dorsal to lateral recumbency (rather than right and left recumbency individually), there was no significant difference in complication rates;

Post-anesthetic temperature—Horses with a lower rectal temperature after recovery were more likely to develop GI dysfunction; and

Time to first passage of feces—Horses with a prolonged time to the first passage of feces after anesthesia were more likely to develop GI dysfunction.

Nelson said some of the study's limitations were that the anesthetic procedures weren't standardized, different attending clinicians have different protocols, and cases were only monitored for 24 hours (meaning some cases could have been missed).

So should owners avoid putting their horses though procedures necessitating general anesthesia? Not necessarily, Nelson said.

"The results of this study should not make horse owners more or less wary of putting their horse under anesthesia, but more informed on potential complications that can occur," he explained. "Although it was very rare for a horse to not survive the anesthetic event, there is always risk of a complication, as no procedure is without risk. Luckily, the GI dysfunction that developed following anesthesia was mostly mild in this population of horses and resolved quickly with prompt medical therapy.

"This study is helpful in educating clients about risks that can occur when their horse has general anesthesia and can guide the veterinarian treating the horse for values to examine in those horses that are at higher risk or develop a complication," he concluded.

About the Author

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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